Gangliosides are membrane-associated glycolipids that have important regulatory roles in many cellular events including differentiation, growth and regeneration. Their concentration is unusually high in neuronal tissue. Active ganglioside synthesis has been found to coincide with periods of intense neuritogenesis and synaptogenesis suggesting that gangliosides play a key role in these processes. We have shown that bovine brain gangliosides mixtures (BBG) enhance axonal sprouting and metabolic activity of primary and established neuronal cell lines. Scanning electron microscopy reveals dramatic changes in surface topography within minutes of ganglioside exposure. The relationship between these surface changes and sprouting is under investigation. An extensive BBG-induced intraneuronal microfilamentous network has been demonstrated with whole-cell electron microscopy. Cytoskeletal disruptive and stabilizing agents are being employed to determine the ultrastructural basis of ganglioside-mediated neuritogenesis. Although eleven different gangliosides increased sprouting of Neuro-2a neuroblastoma, each species elicited morphologically distinct responses. The mechanisms underlying these differences will be examined. The ganglioside GM1 potentiates the action of submaximal levels of Nerve Growth Factor (NGF) on chick sensory ganglia and the adrenal pheochromocytoma PC-12 cells. Liposomal-derived, affinity-purified antibodies directed against the ganglioside GM1 reduce, in a dose-related fashion, NGF-induced axonal sprouting and enzyme induction of these cells. In contrast, antibodies directed against GM2 or GQ1c have almost no effect. These results suggest that membrane-associated ganglioside may function to modulate neurotrophic interactions and have prompted the speculation that the ganglioside GM1 may be specifically involved in the regulation and amplification of NGF. To investigate this hypothesis we will examine the effect of gangliosides and antibodies directed against gangliosides on well defined, in vitro models of neurotrophic interaction. Histochemical and morphological probes, including lectins, toxins, Colcemid and cytochalasin D, will be employed to examine the distribution and fluidity of neuronal membranes as well as the relationship between membrane-associated gangliosides and their cytoskeletal anchorages. These studies will determine the role of gangliosides in neuritogenesis and will provide information on the basic mechanisms of neuronal development and regeneration.